Fig. 2

Bench study. The figure represents dynamic simulated muscle pressure (Pmus)–volume loops recorded with and without the addition of the DAR filter (see text). The change of tidal volume between configurations with and without filter was calculated. The pressure–volume loop with filter was obtained by increasing simulated patient effort to maintain Vt constant (same Vt than in the without filter configuration). The patient work of breathing (WOB patient) was defined as the trapezoidal numerical integration of the pressure–volume curve, which corresponds to the area under the curve. The shaded area represents the relative change in patient’s WOB induced by the filter to keep the Vt constant. ∆P represents the maximum change in muscle pressure between the two configurations. a Dynamic Pmus–volume loops obtained using the Boussignac valve with and without additional filter in the following conditions: moderate simulated effort (10 cm H₂O), low simulated respiratory system resistance (5 cm H₂O/L/s) and CPAP set at 6 cm H₂O. b Dynamic Pmus–volume loops obtained using the Boussignac valve with and without additional filter in the following conditions: moderate simulated effort (10 cm H₂O), high simulated respiratory system resistance (15 cm H₂O/L/s) and CPAP set at 6 cm H₂O